Resumen de Abundancia y diversidad de los invertebrados litorales de isla Socorro, Archipiélago Revillagigedo, México

Silvia R. Mille Pagaza, Jorge Carrillo Laguna, Alicia Pérez Chi, M. E. Sánchez-Salazar

• español

  Se analiza la estructura de la biota macrobentónica litoral de isla Socorro, Archipiélago Revillagigedo, Colima, México en función de la composición, abundancia, diversidad y distribución de las especies de invertebrados en diversos puntos. Durante la primavera de 1991 y de 1992 se efectuaron muestreos en las zonas supra y mesolitoral de ocho bahías, encontrando 161 especies de invertebrados. La densidad más alta (281 org./m2) se registró en la bahía Blanca NE y la mayor diversidad (4.7 bits/individuo) en la bahía Vargas Lozano. La mayoría de las especies se clasificaron como accidentales de acuerdo con la clasificación de frecuencias de Dajoz, las dominantes como accesorias y solamente I. janus, como constante en 1992. La diversidad y la equidad indican que las comunidades más homogéneas son las de las bahías Vargas Lozano y Binners y la más heterogénea la de Grayson. La similitud separa dos grupos de bahías. Uno lo forman las ubicadas al suroeste de la isla y el otro grupo lo conforman las que se encuentran al noroeste de la misma.

• English

  Composition, abundance, diversity and distribution of the littoral benthic invertebrates of Socorro Island with transects (parallel to the coast and with 1 m2 quadrats) were analyzed. During the spring of 1991 and 1992 samples were taken from the upper and middle levels of the intertidal zone in Vargas Lozano, Braithwaite, Blanca SW, Blanca NE, Binners, Grayson, Academia and Norte bays. The 161 species found belong to Porifera, Cnidaria, Platyhelmintha, Nemertina, Sipunculida, Annelida, Mollusca, Arthropoda and Echinodermata. Crustaceans and mollusks were the richest groups in both years, as in other rocky shores. Highest total density was found in Blanca NE bay in both samplings, with 281 orgs./m2 in the first and 172 orgs./m2 in the second. Most frequently found species were Isognomon janus (Mollusca, Pelecypoda), Littorina pullata (Mollusca, Gastropoda), Hipponix panamensis (Mollusca, Gastropoda), Pachygrapsus transversus (Crustacea, Grapsoidea) and Turbo funiculosus (Mollusca, Gastropoda). Because of the complexity of the habitat structure, Vargas Lozano was the bay with the highest specific richness (83 species), greatest diversity (4.7 bits/individual) and lowest dominance (0.065). Most species were classified as accidentals with the Dajoz’s frequency classification, while the dominant species were accessories and only I. janus, in the spring 1991, was a constant species. Two kinds of bays were distinguished: those with some dominant species (density) and those in which there was no evident dominance by a particular species. Consequently, the diversity and evenness values were set apart: homogeneous communities (Vargas Lozano and Binners) and heterogeneous communities (Grayson bay and others), characterized by intermediate evenness values. The Jaccard similarity index identified two regions: one formed by bays found mainly in the southwest part of the island (Binners, Vargas Lozano, Braithwaite, Grayson and Blanca SW) and the other found in the northern region that included Blanca NE, Academia and Norte; however, Blanca NE had the most diverse species composition because of its physiographic particularities and because the sediment retained by the filamentous algae on the flat stones allow many species to settle down. Isognomon janus, Mitrella baccata (Mollusca, Gastropoda), P. transversus and Xanthodius cooksoni (Crustacea, Xanthoidea) were the most common species in all bays in both expeditions. The dominance-diversity relationship, the high specific richness and the low dominance of coastal invertebrates from the different bays, are indicative that the communities in Socorro Island are little disturbed; their specific richness are similar to those of coral reefs.